Snapshots; Cloning - Dell PS4000 Configuration Manual


Be aware of an application's data usage patterns. Some applications perform automated disk
optimization that may cause a thin provisioned volume to use more physical storage than would
be needed for normal operations. For these types of applications, thin provisioned volumes may
not be indicated.

Use ―quick format‖ options when formatting OS file systems that are hosted by thin provisioned
volumes.

Thin provisioned volumes should not be used for hosting OS boot partitions or OS page file
cache.
3.3.4

Snapshots

Snapshots are point in time copies of volumes. Snapshots have some features and properties similar to
volumes as well as some unique capabilities. Like volumes, snapshots can be assigned an iqn and
presented as volumes to a host. This allows hosts to mount a snapshot, potentially change the data in
the snapshot, or convert it to a real volume (clone) that has dedicated space allocated to it from the
free storage pool.
Snapshots require that space be reserved during volume creation (or after volume is created) to store
the snapshot(s) created from that volume. All snapshot reserve space for a specific volume always
resides in the same storage pool as the volume. By default, Group Manager allocates snapshot reserve
space equal to 100% of the host volume's allocated space. This ensures that a 100% data change in the
volume can be protected by a single snapshot. This value can be set to a lower value based on the
application's data change rate, snapshot/backup plan, or role that the snapshot will be used. The
following items should be considered when determine the size of a volume's snapshot reserve:

Data change rate for the application(s) who is using the volume

Defragmentation policy of the OS or application using the volume

The role or purpose for creating the snapshot(s).
Snapshots have the following characteristics:

They are identified using names that consist of the parent volume name plus a date/time
stamp indicating when the snapshot was created as a default name.

If name of parent volume changes, existing snapshots iqn names do NOT change accordingly,
but retain their original iqn name.

Deleting a snapshot's parent volume deletes all associated snapshots for that volume.

Snapshots of volumes with a high data change rate will require a larger snapshot reserve space.

Snapshots have access control lists that are inherited from the parent volume by default.

Snapshot reserve space for any volume can be decreased at any time. The minimum size
allowed will be based on the current space usage consumed by existing snapshots using the
snapshot reserve.

Snapshot reserved space for any volume can be increased at any time assuming there is
available free space in the storage pool hosting the volume.
3.3.5

Cloning

Cloning creates a new volume by copying an existing volume. The new volume has the same reported
size, contents and thin-provision settings as the original volume. You can clone a regular volume, a
specific replica of a volume, or a specific snapshot of a volume.
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